1. Field of the Invention
The present invention relates to an electric injection apparatus, and more particularly to an electric injection apparatus which carries out back pressure control in metering by means of hydraulic power.
2. Description of the Prior Art
There have been already known some electric injection apparatuses that carries out back pressure control by means of hydraulic pressure. One of the prior art is to couple the rear end of an injection screw to a piston in a cylinder formed at the center of a screw thrust member so that the backward force of the screw is controlled by hydraulic pressure. In such a conventional electric injection apparatus, the injection screw transfers heat to heat the hydraulic fluid in the cylinder easily. Therefore, long-hour use heats up the hydraulic fluid with viscosity decrease, causing a problem of variations in the set pressure. In addition, since the hydraulic cylinder is provided inside, the screw thrust member is troublesome to fabricate. Accordingly, there is also the problem of hard adoption for electric injection apparatuses of ordinary structure.
In another example of the prior art, hydraulic cylinders are arranged across the support and the screw thrust member of the injection apparatus to carry out backpressure control. The cylinders are integrated onto both sides of the screw thrust member, and their piston rods are coupled to the support. Therefore, as in the conventional apparatus described above, it is inevitable that the heat transfer through the injection screw thermally affects the hydraulic fluid in the cylinders. Besides, like the preceding prior art, there is the problem of hard adoption for electric injection apparatuses of ordinary structure.